It is known to provide control systems in the textile arts to control spinning or twisting machines or frames which can have two separately supplied electric motors driving respective loads and fed with mains or line voltage--i.e. a relatively high voltage by comparison with that which may be used for control purposes--and high current.
While the invention will be described and has been found to be particularly useful for ring-spinning and ring-twisting frames, the principles are equally applicable to other spinning and twisting machines and textile machinery such as drafting frames, flyer, OE and doubler spinners and twisters and the like in which a plurality of electric motors are used and wherein one or more must be brought from the operating speed to standstill.
With ring spinning machines, it has already been recognized that a reduction in speed from the normal operating speed to standstill should not be effected simply by shutting off the motor involved, but rather that a control circuit for shutdown purposes should be used to initially reduce the speed to a predetermined lower level, e.g. such that the spindles are driven at about only 8000 rpm, a considerable reduction from the normal operating speed. After the reduced but still substantial speed is reached, the circuit simultaneously cuts off all of the relevant motors and, at the same time, actuates respective brakes so arrayed with respect to even the slowest system to reach standstill that substantially all of the motors and the respective loads reach standstill simultaneously.
This ensures that the spindles will not reach standstill before the drafting rollers or vice versa so that yarn breakage is minimized.
Conventional automatic shutdown systems of this type operate, however, only as long as the system is supplied by the mains or line current. They completely fail upon sudden power failures in the line or mains. In such cases, the motors are deenergized in fractions of a second and the apparatus is brought practically instantaneously to standstill in a totally uncontrolled manner resulting in numerous yarn breakages and other damage to the yarn, rovings and filaments.